Stacking Two Triads

A really effective way to create interesting harmonic structures is to stack two triads on top of each other. This procedure is called polychords, bitonal chords or under certain conditions upper structure triads.

Depending on what chords you stack you can create either quite consonant harmonic structure but also very dissonant sounds. One of the most prominent polychords is probably the Matrix Chord. A C-major triad in the trumpets gets stacked over an E-minor triad in the horns (starting at 0:05 in the Youtube video). The most important thing to know about these polychords is, the simpler the two chords, the easier to understand they are.

In the case of Matrix, our brain can easily distinguish between the two triads because it is very used to identifying and hearing triads but gets the feeling of the interesting overall harmony. What helps to distinguish even further is the dynamic shaping of these chords as well as the two different instrumental colours.